When you start a game, play a little and go somewhere else on device while leaving the game running in background (Chrome's tab) and/or locking and unlocking the device and then coming back to the game - the game sometimes totally loses all sound and goes silent and only refreshing the game works.

This happens on both iOS and Android devices.

Tried many things and looks like it's mostly browser/OS thing but maybe someone knows the solution for this problem?

Looks like when the game's tab makes no sounds for a longer time - Chrome stops the sounds permanently for this tab. Even if you come back and do something that makes sounds in particular game - the game is irreversably muted and as i said before - only refreshing makes the sounds to work again.

***Looks like when the game's tab makes no sounds for a longer time - Chrome stops the sounds permanently for this tab (if not active). Even if you come back and do something that makes sounds in particular game - the game is irreversably muted and as i said before - only refreshing the game makes the sounds to work again.***

Make sure you're using the latest release which includes bug fixes for audio, particularly on iOS 9.

I can't really help from the information you've provided. If you think something is wrong with C2, please file a bug report following all the guidelines. I've seen previously that your site had the wrong MIME types set up, and note that can also cause audio to fail to play in some circumstances.